Walking beam conveyor

ABSTRACT

A walking beam conveyor of the kind which comprises a series of stationary beams and a series of walking beams which have a driving mechanism by which they are moved upwards relative to the stationary beams to lift workpieces therefrom, then longitudinally to convey the workpieces along the stationary beams and subsequently downwards again to replace the workpieces on the stationary beams is provided with a mechanism for raising and lowering the walking beams in such a way as to minimize the impact of the working beams on the workpieces as they raise the workpieces from the stationary beams. This mechanism includes a number of hydraulic fluid pressure operated cylinders which are connected to the walking beams and operate successively. A number of the cylinders move the walking beams upwards until they come into contact with the workpieces and are then stalled. One or more further cylinders are then brought into operation in sequence until there are sufficient cylinders to increase the force acting on the walking beams until the walking beams are able to lift the workpieces from the stationary beams after which the walking beams are moved longitudinally by a further hydraulic fluid pressure operated cylinder and the beams are then lowered again.

United States Patent Brockmann [54] WALKING BEAM CONVEYOR [72] lnventor:Heinz Brockmann, Dusseldorf-Gallberg,

Germany [73] Assignee: Brockmann & Bundt Industrle-Ofenbau,

Dusseldorf, Germany [22] Filed: July 2, 1970 [21] Appl. No.: 51,813

[30] Foreign Application Priority Data Jan. 12, 1970 Germany ..P 20 01052.0

[52] U.S.Cl ..198/219 [51] Int. Cl. r ..B65g 25/04 [58] Field ofSearch..198/219; 60/5l,52 HF, 221

[56] References Cited UNITED STATES PATENTS 2,224,956 12/1940 Ernst etal... ...60/52 HF 3,322,259 6/1967 Millazzo. 198/219 3,355,008 11/1967Milazzo ..198/219 3,369,650 2/1968 Caretto et al.. ..198/219 3,451,5326/1969 Manterfield... ..198/219 1,965,868 7/1934 Vickers ..198/219Primary Examiner-Evon C. Blunk Assistant Examiner-H. S. LaneAttorney-Arthur O. Klein [5 7] ABSTRACT A walking beam conveyor of thekind which comprises a series of stationary beams and a series ofwalking beams which have a driving mechanism by which they are movedupwards relative to the stationary beams to lift workpieces therefrom,then longitudinally to convey the workpieces along the stationary beamsand subsequently downwards again to replace the workpieces on thestationary beams is provided with a mechanism for raising and loweringthe walking beams in such a way as to minimize the impact of the workingbeams on the workpieces as they raise the workpieces from the stationarybeams. This mechanism includes a number of hydraulic fluid pressureoperated cylinders which are connected to the walking beams and operatesuccessively. A number of the cylinders move the walking beams upwardsuntil they come into contact with the workpieces and are then stalled.One or more further cylinders are then brought into operation insequence until there are sufficient cylinders to increase the forceacting on the walking beams until the walking beams are able to lift theworkpieces from the stationary beams after which the walking beams aremoved longitudinally by a further hydraulic fluid pressure operatedcylinder and the beams are then lowered again.

5 Claims, 6 Drawing Figures Patented May 30, 1972 3,666,086

3 Sheets-Sheet l W 140 12u--\ M /NVENT0R y, He/nz BROCK/7/ l lv MawAttorney Patented May 30, 1972 3 Sheets-Sheet 2 INVENTOR HeinzBROfiK/M/VI m a m Altarnev Patented May 30, 1972 3,666,086

3 Sheets-Sheet 3 FlG 5 INVENTOR BY: l/emz BROCKNAIVA/ mag/;

WALKING BEAM CONVEYOR This invention relates to walking beam or jiggingconveyors, which may be used for example for conveying workpiecesthrough a tunnel furnace. Such furnaces with conveyors are usuallycalled walking grate or jigging grate furnaces.

Walking beam conveyors have two groups of beams, one of which moves. Theworkpieces initially rest on the other fixed group of beams. The movingbeams rise upwards under the workpieces, lift them, convey them througha certain distance in the direction of conveyance and then deposit theworkpieces back again on to the other group of beams. The moving beamsfinally return to their initial positions. Each group of beams rests incontact with the workpieces for a limited period only, for exampleduring only half of the time taken by the workpieces to move through thefurnace. This fact makes walking beam conveyors particularly suitablefor conveying hot workpieces.

When a walking beam conveyor is in operation the moving group of beams,that is to say the walking beams, move upwards under the workpieces,during the first phase of their movement, until they come into contactwith the under sides of the workpieces, before lifting the workpiecesfrom the upper faces of the fixed beams. At the instant when the walkingbeams make contact with the under sides of the workpieces a considerableimpact can occur. This impact not only shortens the life of the walkingbeam conveyor, but, when the conveyor is part of a furnace, also damagesthe refractory lining of the furnace. A number of methods have thereforebeen proposed to prevent this impact. However all these proposed methodsuse as their starting point an instant when the two groups of beams areat the same height. This height remains constant until, after a periodof operation, the two groups of beams become worn down differently, andbecome encrusted with scale, particles and the like. After that theinstant when the two groups of beams are at the same height becomesincreasingly displaced and the basis of the proposed methods is nolonger valid.

The object of the present invention is to provide a walking beamconveyor in which this impact is reduced and which is useful for therough operating conditions prevailing in a walking grate furnace.

According to this invention the walking beams of such a conveyor aredriven in their upward and downward movements by a plurality ofhydraulic fluid pressure operated pistons at least one of which issupplied with fluid from a hydraulic accumulator. The function of thehydraulic accumulator driven piston is to compensate the weight of thewalking beams, at least to a large extent, so that the walking beams canbe lifted from their initial positions up towards the workpieces on thefixed beams by correspondingly less lifting thrust from the otherpistons, which may be called the lifting pistons. The effect obtained isthat the impact produced when the walking beams make contact with theworkpieces is considerably reduced.

The impact can be still further reduced, by using several hydraulicaccumulator-operated compensating cylinders with a control valveinterposed between each compensating cylinder and the accumulator. Thecontrol valves are actuated independently of each other. There aretherefore a number of compensating pistons and a number of listingpistons. The lifting pistons move the walking beams upwards and overcomefriction and the like, but support only a very small part of the walkingbeam weight. The accumulator operated compensating pistons, on the otherhand, take the weight, or most of the weight, of the walking beams andsubsequently of the workpieces. The control valves are openedsuccessively in response to the amount of lifting thrust required toraise the workpieces from the fixed beams, that is to say withincreasing lifting thrust required more of the control valves areopened, bringing into action more of the accumulator operatedcompensation pistons. After a first phase of the upward movement, inwhich the walking beams rise upwards from their initial positions, thereis a second in which the workpieces are lifted from the fixed beams. Forthis second phase of the movement further accumulator operatedcompensating pistons are brought into operation, in addition to thosewhich have hitherto supported the weight of the walking beam. The extracompensating pistons take the weight of the workpieces and consequentlythe lifting thrust supplied by the lifting piston is now sufficient tolift the workpieces, as well as the walking beams. Finally theworkpieces are moved along horizontally, without touching the fixedbeams.

At the end of the horizontal movement the workpieces are lowered againand deposited on the fixed beams. This is brought about by releasing thepressure in the lifting cylinders, with the result that the weight ofthe workpieces together with the weight of the walking beams becomesgreater than the lifting thrust applied by the accumulator operatedcompensating pistons. The walking beams, with their load of workpieces.consequently move downwards, expelling fluid from the compensatingpistons back into the accumulator.

When the workpieces come to rest on the fixed beams the control valveswhich were last actuated are returned to their initial positions,disconnecting the compensating pistons used for compensating theworkpiece load. This leaves only those compensating pistons stilloperating which are used for compensating the weight of the walkingbeams. However as already mentioned these compensating pistons do notentirely support the weight of the walking beams, and consequently thewalking beams continue to move downwards, hydraulic fluid being expelledfrom these compensating cylinders, back into the accumulators. When thewalking beams and all the pistons have returned to their initialpositions the accumulator pressure has also regained its initial value,less whatever pressure loss may have occurred due to friction andleakages. If the next cycle of operations is not due to beginimmediately, the walking beam conveyor can now be stopped. The threephases of the vertical movements of the walking beams have now beencompleted, that is to say the first upward movement of the walking beamsfrom their initial positions; the lifting of the workpieces and thedepositing of the workpieces back onto the fixed beams, and it should beobserved that each of these three phases is initiated by actuation ofthe control valves for the accumulator operated compensating cylinders.

Preferably at least percent of the upward thrust in all phases of thevertical movements is provided by the accumulator operated compensatingcylinders, and consequently the impact produced when the walking beamsmake contact with the workpieces is negligibly small. A furtheradvantage compared with previous walking beam conveyors is that theconsumption of energy is less. This represents a considerable saving inoperating costs even if the workpiece load is only a few tons. Duringthe downward movements of the workpieces and walking beams the potentialenergy is not merely converted into heat but is converted back againinto pressure energy. Two advantages are obtained, in the first placeoperating costs are saved because the energy is not wasted, and secondlyit is unnecessary to provide arrangements for removing heat.

Losses of hydraulic fluid, by leakage and the like, are made up bysupplying fresh hydraulic fluid to the accumulators.

In the preferred example of the invention, separate drives are providedfor the upward and downward, and horizontal movements of the walkingbeams. The cylinders for bringing about the upward and downwardmovements of the walking beams act horizontally on a common transversebeam which drives lifting carriages, each of which runs on a slopingrail and is equipped with rollers which lift the walking beams. Thelifting movement depends on the slope of the rail, giving a mechanicaladvantage which is preferably exploited to allow the walking beams to belifted by cylinders of comparatively short stroke.

The transverse beam is preferably provided with a parallel guide systemwhich ensures that all the walking beams are moved synchronously. Theparallel guide system is of very simple construction, consisting of arocking shaft extending parallel to the transverse beam and rotating inend bearings.

The rocking shaft is connected to the transverse beam by linkages spacedapart along the length of the transverse beam.

According to a further feature of the invention, the separate drive forbringing about the horizontal movements of the walking beams includes atleast one hydraulic cylinder, the movements of which are determined by asliding crank system with a crank arm which rotates at constant speedand an oscillating arm which performs a sine-wave oscillation. Thehorizontal movements of the walking beams follow this sinewaveoscillation and therefore take place smoothly and without any jerking,that is to say without abrupt changes in velocity. When the conveyor isin operation this smooth horizontal oscillation is combined with theimpact free vertical movements of the walking beams so that in theentire operation of the conveyor all movements are smooth and free fromdestructive impacts and abrupt accelerations. Both the conveyor and alsothe furnace, if the conveyor is mounted in one, therefore have longworking lives.

The sine-wave oscillations of the oscillating arm are transmitted to thehorizontally acting cylinder for bringing about the horizontal walkingbeam movements by means of a potentiometer bridge circuit which has twovariable resistors with sliding electric contacts, one actuated by theoscillating arm and the other by the piston of the cylinder. Theoscillating arm is pivoted on a bearing block which is adjustable inposition relative to the crank arm. Adjustment of the position of thebearing block alters the amplitude of oscillation of the oscillating armand therefore the amplitude of the horizontal oscillation of the walkingbeams.

An example of a conveyor constructed in accordance with the invention isillustrated in the accompanying drawings, in which:

FIG. 1 is a diagrammatic side view of a walking grate furnace, with anumber of fixed beams and a number of walking beams, each walking beammoving both vertically and horizontally;

FIG. 2 shows a driving mechanism for lifting and lowering the walkingbeams;

FIG. 3 shows a detail of the mechanism of FIG. 1;

FIG. 4 shows a control system for controlling the horizontal movementsof the walking beams;

FIG. 5 shows a hydraulic control system for controlling the mechanismshown in FIGS. 2 and 3; and,

FIG. 6 shows an electrical circuit which cooperates with the controlsystem shown in FIG. 4.

FIG. 1 shows a walking grate furnace with a furnace hood 1 a feed rollerconveyor 2, a delivery roller conveyor 3, fixed beams 4 and walkingbeams 5. Each walking beam 5 has a lower rail 5a which has an extensionconnected through a joint 5b to a piston rod 60 of a driving piston in acylinder 6, which is pivotally mounted in a pivot block 7. The axis ofthe piston is in line with the axis of the lower rail 50 so that whenthe conveyor is in operation the piston gives the lower rail 5a and withit the walking beam 5 a horizontal reciprocating movement.

Each walking beam 5 is moved vertically, to lift and lower it, by alifting carriage 8 which comprises a housing 8a containing rollers 8b,8c, 8d which rotate on axes extending across the longitudinal axis ofthe lower rail 50. The roller 8b runs on a horizontal rail 9. The roller8d runs on an inclined rail 10 in the form of a wedge-shaped structure.The roller 80 supports the lower rail 5a.

Each lifting carriage 8 is moved by one end of a tension rod 11 theother end of which is attached to a traction carriage 12 (FIG. 2)comprising a transverse beam 120 equipped with brackets 12b. Thetransverse beam 120 is equipped at each end with four wheels 12carranged in two pairs. One pair of wheels is supported directly by thetransverse beam 12a, the other pair being supported by the brackets 12b.The brackets 12b form together with the transverse beam 12a a U-shapedstructure arranged to prevent the traction carriage 12 from tippingover. The wheels 12c are guided between guides 13 arranged so that thetraction carriage 12 can travel only horizontally. In order to ensurethat the traction carriage 12 always remains positioned transversely,and cannot adopt a skew position, which would give different movementsto the various walking beams, and might even stall the drive, thetraction carriage 12 is guided in its movement by a parallel guidesystem comprising a rocking shaft 14a which rocks in bearings at its twoends. The rocking shaft 14a has crank arms 14b and links connected tothe transverse beam 12a. The traction carriage 12 is reciprocated by asystem of pistons in cylinders 15 and 16, the pistons being connected tothe transverse beam 12a by connecting rods 15a and 16a.

With regard to the horizontal movements of the walking beams 5, FIG. 4shows a simulator the movements of which govern the movements of thedriving pistons in the cylinders 6. For this purpose the simulator acts,with a suitable gearing effect, through an electro-hydraulic controlcircuit. The simulator is essentially a sliding crank system including acrank arm 17 driven by a motor which is not shown in the drawing. Asliding sleeve 18 is pivoted on the crank arm 17 and slides on anoscillating arm 19 pivoted to a bearing block 20 which is adjustable inheight. The oscillating arm 19 is in the form of a rod along which thesleeve 18 slides.

The bearing block 20, which is adjustable in height, moves on rollers20a and is driven by an adjustment drive 20b, which can if desired beremote controlled and can be actuated hydraulically or if desiredmanually. For example the adjustment drive 20!) can be operated througha threaded spindle which provides an irreversible drive giving aself-locking ef' feet.

The electro-hydraulic control circuit shown in FIG. 6 includes apotentiometer bridge circuit with a measured value potentiometer 21b anda desired value potentiometer 21a. The potentiometer bridge circuit hastwo upper legs, such upper legs having resistances which areschematically shown in R and R respectively. The measured valuepotentiometer 21b has a sliding contact connected to the piston in thecylinder 6. The desired value potentiometer 21a has a sliding contactconnected to the sliding crank system. The two potentiometers 21a and21b actuate a telescoping coil system 24 containing a permanent magnetarmature 22 which forms part of a four-way slide valve 23 with edgecontrol, which controls the movements of the piston in the cylinder 6.Consequently any voltage difference between the desired valuepotentiometer 21a and the measured value potentiometer 21b moves thearmature 22, actuating the slide valve 23 and so causing the piston inthe cylinder 6 to follow up movements of the upper end of the arm 19.

When the conveyor is in operation the workpieces, which are not shown inthe drawing, reach the walking grate furnace A on the feed rollerconveyor 2, which conveys them to the fixed beams 4 and the walkingbeams 5. The workpieces are conveyed intermittently through the furnaceA by the walking beams 5 to the delivery roller conveyor 3. To bringthis about, the walking beams 5 lift the workpieces from the supportingupper surfaces of the fixed beams 4, convey them horizontally forwardsthrough a certain distance, determined by the stroke of the piston inthe cylinder 6, and then lower them again onto the surfaces of the fixedbeam 4. This operation is repeated, step by step, until the workpiecesreach the delivery roller conveyor 3, which takes them away. Themovements of the walking beams follow an approximately rectangular path,or a distorted rectangular path somewhere between a rectangle and acircle. The shape of this path can be varied within wide limits bysuitably adjusting the controls for the vertical and the horizontalmovements of the walking beams.

The horizontal movements of the walking beams are determined by thesliding crank system, shown in FIG. 4. Assuming that the crank 17 isrotating at constant speed the oscillating arm 19 performs a sine-waveoscillation. The horizontal oscillations of the walking beam 5 thereforetake place smoothly and evenly, that is to say without any abruptchanges in velocity. The length of the stroke of this horizontaloscillation can be adjusted steplessly by stepless vertical adjustmentin position of the bearing block 20, that is to say by steplessadjustment of the amplitude of oscillation of the oscillating arm.

On the other hand, the lifting and lowering movements of the walkingbeams 5 are produced by the movements of the lifting carriage 8. Thelifting carriage 8 moves horizontally and at the same time vertically,due to the slope of the upper surface of the wedge-shaped rail 10, withthe result that the lifting carriage 8 lifts and lowers the walkingbeams 5. In the present example the vertical movements of the walkingbeams 5 are directly proportional to the horizontal movements of thelifting carriage 8, and consequently the forces applied by the pistonsof the driving cylinder and 16 are applied as lifting forces to thewalking beams 5 after being increased or reduced by a factor whichdepends on the slope of the wedge-shaped rail 10.

The vertical movements of the walking beams 5 take place in severalstages. In the first stage the walking beams 5 are accelerated upwards,the driving mechanism, including the tension rods 11, being acceleratedfrom their initial positions. In the second stage of the movement theworkpiece is accelerated upwards from the supporting surfaces of thefixed beams 4, the driving mechanism also being accelerated. In thethird stage of the movement the workpiece is lowered again onto thefixed beams 4 and in the fourth stage the walking beams 5 move downwardsagain to their initial positions.

During the initial acceleration of the walking beams and of the drivingmechanism, including the tension rods 11 from their initial positions,that is to say from their positions of rest, the energy which has to besupplied to effect the accelerations is reduced in that some of thepistons in the cylinders 16 constantly apply a thrust which largelycompensates for the weight of the walking beams 5, the energy for thisthrust being derived from a hydraulic accumulator as shown in FIG. 5. Inthe present example approximately 90 percent of the weight of thewalking beams is supported in this way. Consequently the walking beams 5are lifted quite gently upwards by the piston in the lifting cylinder 15until they come into contact with the workpiece resting on the fixedbeams 4. The effect obtained is that when the walking beams 5 makecontact with the workpieces, the impact produced is negligibly small. Assoon as the walking beams 5 come into contact with the workpieces thewalking beams are immediately brought to a standstill, because thelifting cylinder 15 applies only a small amount of thrust. As soon asthis occurs, that is to say as soon as the walking beams have beenbrought to a standstill, by coming into contact with the workpieces,pressure builds up in the lifting cylinder 15, actuating a pressuresensitive switch 27 and further excess pressure is then released by anover pressure release valve 26. The pressure sensitive switch 27delivers a control pulse which opens successively a series of valves 28connecting the accumulator 25 to the remaining thrust cylinders 16 whichhave not hitherto been used for compensating the weight of the walkingbeams 5. The valves 28 are opened one after the other to the effect thatthe lifting thrust applied to the walking beams is increased onlygradually and almost continuously until the workpiece is lifted from thesupporting surfaces of the fixed beams 4.

The valves 28 can be opened in the desired sequence by various devices.The sequence can be determined electrically by using switching relays.Alternatively, using a mechanical device, the pressure sensitive switch27 opens the first valve 28, bringing the first piston into movement inits thrust cylinder 16. This piston actuates mechanically a simple limitswitch, which opens the next valve 28. On the other hand if desired thesimultaneous movements of the other pistons in the cylinders 16 can beutilized. All the pistons move with the transverse beam 12a. Each pistoncan therefore trip its own limit switch. The sequence in which thevalves 28 are opened depends of course on the pressure characteristiccurve of the accumulator 25.

In other examples of the invention, not shown in the drawings, eachthrust cylinder 16 has its own accumulator. Moreover if desired anynumber of accumulators can be used, the cylinders 16 being connectedtogether and the accumulators connected in sequence with interposedcontrol valves. Finally each cylinder 16 can if desired have severalaccumulators, connected in sequence with interposed control valves. Thisarrangement has the advantage that the decreasing pressure in anaccumulator, resulting from the movement of the piston in the cylinder16, is compensated by bringing in a further accumulator.

In the present example there are enough thrust cylinders 16 to handlethe highest workpiece load for which the conveyor is designed. When asmaller workpiece load is being conveyed only some of the thrustcylinders 16 are brought into operation. This can be done for example bythe operator by switching off some of the valves 28 by remote control onthe basis of a program. Alternatively the thrust cylinders 16 can beselected automatically. For this purpose each thrust cylinder 16 isequipped with a pressure sensitive switch which responds to an upperlimiting pressure and a lower limiting pressure and these switches bringthe thrust cylinders 16 into operation successively at brief intervalsuntil the pressure in the thrust cylinders 16 no longer rises to theupper limiting pressure of the pressure sensitive switch.

During the lifting operation, only those thrust cylinders 16 are inaction which are just necessary to allow the lifting cylinder 15 to liftthe existing workpiece load. To lower the workpiece back onto the fixedbeams 4 it is therefore merely necessary to release the pressure in thelifting cylinder 15. The weight of the workpiece load, plus the weightof the walking beams, is then sufficient to expel fluid from the thrustcylinders 16 back into the accumulator 25, the walking beams 5 gentlylowering the workpieces onto the surfaces of the fixed beams. In thisoperation the pressure in the accumulator 25 increases back again to itsinitial value. After the workpieces have come to rest on the fixed beamsthe walking beams continue to move downwards, because the lifting thrustapplied by the trust cylinders 16 which are still in operation is alittle less than the .weight of the walking beams. Consequently thewalking beams move downwards to their initial positions, hydraulic fluidbeing expelled from the remaining thrust cylinders 16 back into theaccumulator 255. Finally the pressure in the accumulator 25 returns toits initial value and the walking beams 5 return to their initialpositions.

In the case where frictional resistances impede the lowering of theworkpieces onto the fixed beams, the downward movement of the walkingbeams 5 can be power assisted. For this purpose, in the present example,the lifting cylinder 15 is made double-acting. During the liftingmovement hydraulic fluid admitted to the cylinder chamber behind thepiston drives the piston outwards, whereas during the lowering movement,for example after the workpieces have been deposited on the fixed beams,fluid is admitted to the cylinder chamber in front of the piston and isexhausted from the cylinder chamber behind the piston, so that thewalking beams 5 are lowered to their initial positions under power.

The control valves which connect the accumulator 25 to the liftingcylinders 15 are preferably program controlled slide valves the reversalperiod of which can be steplessly adjusted by a throttle, so that thevertical movements of the walking beams are smooth and gentle when theworkpieces are being lifted from the fixed beams 4 and lowered back ontothem.

I claim:

1. In a walking beam conveyor including a plurality of stationary beams,a plurality of walking beams, means mounting said walking beams forupward and downward movement relative to said stationary beams andreciprocating longitudinal movement relative to said stationary beams,driving mechanism for moving said walking beams in said upward anddownward movement and driving mechanism for moving said walking beams insaid reciprocating longitudinal movement, the improvement wherein saiddriving mechanism for moving said walking beams in said upward anddownward movement includes a plurality of hydraulic fluid pressureoperated cylinders and drive pistons, means operatively connectingsaidcylinders to said walking beams, means for supplying hydraulic fluidunder pressure to some of said cylinders and independent means forsupplying hydraulic fluid under pressure to one other of said cylinders,said means for supplying hydraulic fluid to said some of said cylindersincluding hydraulic accumulator means and means operatively connectingsaid hydraulic accumulator means to at least one of said some cylinders,the force of the accumulator-driven drive pistons before the impact ofthe walking beam onto the work piece on the conveyor being at a maximumequal to the weight of the walking beam, including means operativelyconnecting said hydraulic accumulator means to a plurality of said somecylinders, said connecting means including a plurality of control valvesand means connecting said valves individually to said cylinders andmeans for independently actuating said control valves, the latter meansincluding means responsive to a workpiece load on said walking beams andmeans for actuating said valves to operate said cylinders in sequence independence upon the magnitude of said load.

2. ln a walking beam conveyor including a plurality of stationary beams,a plurality of walking beams, means mounting said walking beams forupward and downward movement relative to said stationary beams andreciprocating longitudinal movement relative to said stationary beams,driving mechanism for moving said walking beam in said upward anddownward movement and driving mechanism for moving said walking beams insaid reciprocating longitudinal movement, the improvement wherein saiddriving mechanism for moving said walking beams in said upward anddownward movement includes a plurality of hydraulic fluid pressureoperated cylinders, means operatively connecting said cylinders to saidwalking beams, means for supplying hydraulic fluid under pressure tosome of said cylinders and independent means for supplying hydraulicfluid under pressure to one other of said cylinders, said means forsupplying hydraulic fluid to said some of said cylinders includinghydraulic accumulator means and means operatively connecting saidhydraulic accumulator means to at least one of said some cylinders, saiddrive mechanism for moving said walking beam in said horizontalreciprocating movement including at least one hydraulic fluid pressureoperated cylinder, a piston in said cylinder, means connecting saidpiston to said walking beams, and means for controlling the operation ofsaid cylinder to cause said piston to perform a reciprocating movement,said controlling means including a sliding crank mechanism and means forcausing said piston to follow movements of said sliding crank mechanism.

3, A walking beam conveyor as claimed in claim 2, wherein said means forcausing said piston to follow movements of said sliding crank mechanisminclude an electrical potentiometer bridge circuit, two variableresistors in said circuit, means connecting one of said variableresistors to said sliding crank mechanism and means connecting the otherof said variable resistors to said cylinder to bring about movements ofsaid piston.

4. A walking beam conveyor as claimed in claim 3, wherein said variableresistors are electric sliding contact resistances, the sliding contactsof which are actuated by said sliding crank mechanism and said piston,

5. A walking beam conveyor as claimed in claim 2, wherein said slidingcrank mechanism includes a rotary crank, an oscillating arm operativelyconnected to said crank, means pivotally mounting one end of saidoscillating arm and means for adjusting said pivotal mounting means,said adjusting means including means for moving said pivotal mountingmeans towards and away from said crank to adjust the length of theoscillating movement of said arm.

1. In a walking beam conveyor including a plurality of stationary beams, a plurality of walking beams, means mounting said walking beams for upward and downward movement relative to said stationary beams and reciprocating longitudinal movement relative to said stationary beams, driving mechanism for moving said walking beams in said upward and downward movement and driving mechanism for moving said walking beams in said reciprocating longitudinal movement, the improvement wherein said driving mechanism for moving said walking beams in said upward and downward movement includes a plurality of hydraulic fluid pressure operated cylinders and drive pistons, means operatively connecting said cylinders to said walking beams, means for supplying hydraulic fluid under pressure to some of said cylinders and independent means for supplying hydraulic fluid under pressure to one other of said cylinders, said means for supplying hydraulic fluid to said some of said cylinders including hydraulic accumulator means and means operatively connecting said hydraulic accumulator means to at least one of said some cylinders, the force of the accumulator-drIven drive pistons before the impact of the walking beam onto the work piece on the conveyor being at a maximum equal to the weight of the walking beam, including means operatively connecting said hydraulic accumulator means to a plurality of said some cylinders, said connecting means including a plurality of control valves and means connecting said valves individually to said cylinders and means for independently actuating said control valves, the latter means including means responsive to a workpiece load on said walking beams and means for actuating said valves to operate said cylinders in sequence in dependence upon the magnitude of said load.
 2. In a walking beam conveyor including a plurality of stationary beams, a plurality of walking beams, means mounting said walking beams for upward and downward movement relative to said stationary beams and reciprocating longitudinal movement relative to said stationary beams, driving mechanism for moving said walking beam in said upward and downward movement and driving mechanism for moving said walking beams in said reciprocating longitudinal movement, the improvement wherein said driving mechanism for moving said walking beams in said upward and downward movement includes a plurality of hydraulic fluid pressure operated cylinders, means operatively connecting said cylinders to said walking beams, means for supplying hydraulic fluid under pressure to some of said cylinders and independent means for supplying hydraulic fluid under pressure to one other of said cylinders, said means for supplying hydraulic fluid to said some of said cylinders including hydraulic accumulator means and means operatively connecting said hydraulic accumulator means to at least one of said some cylinders, said drive mechanism for moving said walking beam in said horizontal reciprocating movement including at least one hydraulic fluid pressure operated cylinder, a piston in said cylinder, means connecting said piston to said walking beams, and means for controlling the operation of said cylinder to cause said piston to perform a reciprocating movement, said controlling means including a sliding crank mechanism and means for causing said piston to follow movements of said sliding crank mechanism.
 3. A walking beam conveyor as claimed in claim 2, wherein said means for causing said piston to follow movements of said sliding crank mechanism include an electrical potentiometer bridge circuit, two variable resistors in said circuit, means connecting one of said variable resistors to said sliding crank mechanism and means connecting the other of said variable resistors to said cylinder to bring about movements of said piston.
 4. A walking beam conveyor as claimed in claim 3, wherein said variable resistors are electric sliding contact resistances, the sliding contacts of which are actuated by said sliding crank mechanism and said piston.
 5. A walking beam conveyor as claimed in claim 2, wherein said sliding crank mechanism includes a rotary crank, an oscillating arm operatively connected to said crank, means pivotally mounting one end of said oscillating arm and means for adjusting said pivotal mounting means, said adjusting means including means for moving said pivotal mounting means towards and away from said crank to adjust the length of the oscillating movement of said arm. 